The following are proposed: 1) To define the isolated transverse tubule preparation more completely. This is a continuation of an ongoing project to produce intact, purified T tubules of defined origin and purity. To facilitate this a preparation of plasma membrane from skeletal muscle will be compared with T tubules both for biochemical properties and for physical composition. 2) To investigate the permeability of T tubules to ions and solutes and the ability of the T tubule to generate, maintain and release a membrane potential. Pulse labelling will be employed to estimate the influx and efflux permeability of T tubules to Ca2 ions, Na ions, K ions and Cl ions. Membrane potential will be estimated by observing the accumulation of a passively transported, lipid insoluble anion. 3) To observe, describe and define by morphological techniques the isolated triad junction and reconstituted triads. Rapid freezing of the organelles to the temperature of liquid helium will be employed to fix the tissue followed by freeze etch. 4) To identify, isolate and describe the junctional protein or proteins of the skeletal muscle triad. This will include isolation of the spanning material which constitutes the pillars and the anchoring material which forms freeze fracture arrays in the terminal cisternae. 5) To investigate whether the signal for Ca2 ions release from sarcoplasmic reticulum is transmitted through the junctional feet.